For tart shells: In a stand mixer, or working with a pastry cutter or two forks, mix butter, flour and salt until dough becomes crumbly. Add water 2 Tbsp. at a time until consistency is smooth. Wrap dough in plastic wrap and chill for 30 minutes.
Roll out dough on cutting board and cut 3-inch circles using a scalloped cookie cutter. Place into greased cupcake pan, pressing sides of dough to fit.
Combine all filling ingredients in a heavy non-aluminum saucepan. Cook over medium-low heat, stirring constantly, until butter is melted and mixture thickens slightly. DO NOT ALLOW TO BOIL. Remove from heat, transfer to a bowl and cool. Pour filling into dough cups and bake 15 to 18 minutes in a preheated 400-degree oven.
Let cool, then top with whipped topping. Refrigerate any leftovers. WHAT LEFTOVERS?